LAN emulation is a concept that is used to interconnect physically different networks that are separated by one or more routers and still make them appear to the connected hosts as a single layer 2 network, e.g. an Ethernet LAN. Connected hosts will then benefit from the advantages of having other nodes, servers, etc., connected to the same layer 2 network. This includes e.g. being able to use multicast and broadcast protocols, e.g. service discovery protocols, in a well-known home LAN environment.
According to existing technology an emulated LAN is created by setting up a mesh of layer 2 tunnels between edge routers in the involved networks, so that layer 2 frames can be transported transparently between the networks. One tunneling mechanism that can be used for this purpose is described in “Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture” by S. Bryant et al., published in March 2005 as Request For Comments 3985 by the Internet Engineering Task Force. According to this mechanism the essential attributes of a telecommunications service (such as Frame Relay, ATM, Ethernet or TDM) are emulated over a packet switched network. Service specific bit streams, cells or packets are encapsulated and carried in layer 2 tunnels between different Customer Edge Equipment (CE). The CEs will be unaware of the emulated service. They will experience the emulated service as an unshared link or circuit of the particular service that is being emulated.
The existing solutions for LAN emulation are designed for a static environment with fixed networks being interconnected. When the dynamic environment of moving networks is introduced the solutions run into problems. There are no mechanisms for dynamically updating the layer 2 tunnels to networks that move between different points of attachment and, similarly, the solutions are not adapted to handle interconnected networks that may connect and disconnect in a more or less arbitrary fashion.
A moving network is defined as a network that is movable in relation to its home network. A moving network can change its point of attachment to a fixed infrastructure or it may have many points of attachment to a fixed infrastructure, but it is still able to communicate with a home network through a mobile router having access to an external access through which all communication nodes in the moving network can communicate. Such a communication node in a moving network is called a moving network node (MNN). In the case of a moving network on e.g. an airplane, the moving network will comprise communication nodes, which may be different users' communication devices, such as laptops, mobile phones, PDAs (Personal Digital Assistants) etc., which communication nodes use wireless or wireline communication to communicate with a mobile router (MR) within the airplane, such that all communication destined to an external address will pass via the mobile router. A moving network may also be e.g. a Personal Area Network (PAN), wherein a PAN comprises all communication devices belonging to a user and situated within short range radio communication distance from each other. In this application, each node in the moving network or connected to the moving network that works like a router for data originating from a moving network node and destined to an address external of the moving network is defined as a mobile router. Examples of such mobile routers are: a PAN device working as a router in a PAN, and a router in a moving network on a vehicle. Note that a node may have both roles, i.e. being both a moving network node and a mobile router, for example a PAN device such as a mobile phone in a PAN.
“The Network Mobility (NEMO) Basic Support Protocol”, by Devarapalli et al, published in January 2005 as a Request For Comments (RFC) 3963 by the Internet Engineering Task Force, identifies a protocol that enables a moving network to attach to different points in the Internet. The protocol is an extension of Mobile IPv6, and allows session continuity for every communication node (or communication device) in the moving network as the moving network moves. It allows a mobile router to maintain a stable network address prefix for a moving network, even as the mobile router changes its, and thus the moving network's, point of attachment to a fixed network infrastructure. This prefix stability is achieved through a solution similar to the Mobile IPv6 solution, i.e. by making a home agent (HA) in the home network of the mobile router a fixed point of presence for the Mobile Router (MR) and maintaining connectivity between the HA and the MR through a tunnel. The address prefix, which is called mobile network prefix (MNP) in the NEMO protocol, is allocated from the address range of the home network, and can thus remain the same even as the MR and its network move. When the MR attaches to a network in a new location, it acquires a new care-of address in the new network, which care-of address is used to locate the MR in the new network, but its home address and address prefix are unchanged. However, just like in Mobile IPv6 the MR has to register its new care-of address in the HA in order to maintain the tunnel between the Mobile Router and the Home Agent. In the NEMO basic support protocol the MNNs will not change their configuration as the MR changes its point of attachment. In other words, the mobility is transparent to the MNNs.